What is a Microcontroller?

A microcontroller (sometimes abbreviated µC or MCU) is a small computer on a single IC containing a processor core, memory, and programmable input/output peripherals.

It is a decision making device used widely in embedded systems and all intelligent devices.

Basic Block Diagram of Microcontroller

Difference between Microcontroller and Microprocessor

Microcontroller has I/O ports, Memory, timers etc all integrated on chip itself

In Microprocessors, I/O ports, memory, timer etc are to be connected externally

Block Diagram to show the difference

What is a 8-bit microcontroller?

8-bit means it can process 8-bit data per clock cycle

It has 8-bit data bus

It can process 1byte of data at a time

AVR ATmega8 Microcontroller

How AVR ATmega8 got its name?

It was developed by Atmel Corporation

AVR implies it belongs to AVR family.

‘8’ in Atmega8 means this microcontroller has 8Kb of flash memory

What is AVR?

AVR is a modified Harvard architecture , 8-bit RISC single chip microcontroller.

It was developed in the year 1996 by Atmel Corporation.

What’s special about AVR?They are fast.

AVR Microcontroller executes most of the instructions in single execution cycle.

AVRs are about 4 times faster than PIC.

They consume less power and can be operated in different power saving modes.

What is RISC?RISC stands for “Reduced Instruction Set

Computer”.

It is a very fast architecture which executes one instruction per clock cycle.

RISC contains very small instruction set.

Programming is easy, but code length increases.

Harvard and Von Neumann Architecture

Harvard Architecture

Harvard architecture has separate data and instruction buses.

This allows transfers to be performed simultaneously on both buses.

Von Neumann Architecture

A Von Neumann architecture has only one bus which is used for both data transfers and instruction fetch

Data transfers and instruction fetches must be scheduled as they cannot be performed at the same time

Introduction to Atmega8

ATmega8 is a low-power CMOS 8-bit microcontroller based on the AVR RISC architecture.

By executing powerful instructions in a single clock cycle, the ATmega8 achieves throughput approaching 1 MIPS per MHz

In order to maximize performance and parallelism, the AVR uses a Harvard architecture.

Features Of ATmega8High-performance, Low-power AVR 8-bit

MicrocontrollerUp to 16 MIPS Throughput at 16 MHz32 x 8 General Purpose Working RegistersInternal Calibrated RC OscillatorExternal and Internal Interrupt SourcesData retention: 20 years at 85°C/100 years at

25°C

Memory Segments

8K Bytes of In-System Self-programmable Flash program memory

512 Bytes EEPROM (Electrically Erasable Programmable Read Only Memory)

1K Byte Internal SRAM (Static Random Access Memory)

Peripheral Features Two 8-bit Timer/Counters with Separate Prescaler, one

Compare Mode. One 16-bit Timer/Counter with Separate Prescaler,

Compare Mode, and Capture Mode. Real Time Counter with Separate Oscillator. Three PWM Channels. 8-channel ADC in TQFP package .

Continued…

6-channel ADC in PDIP package.Byte-oriented Two-wire Serial Interface.Programmable Serial USART.Master/Slave SPI Serial Interface.Programmable Watchdog Timer with Separate

On-chip Oscillator.On-chip Analog Comparator.

TYPES OF PACKAGES

28-lead PDIP (Plastic Dual In-line Package)

32-lead TQFP (Thin Quad film Package)

How ATmega8 PDIP Package looks like?

How ATmega8 TQFP Package looks like?

Pinout of ATmega8

Pin DescriptionVCC: Digital supply voltage 5V.GND: Ground.RESET: A low level on this pin for longer than

the minimum pulse length will generate a reset, even if the clock is not running.

AREF: The analog reference pin for the A/D Converter.

Continued….

AVCC : The supply voltage pin for the A/D Converter, Port C (3..0).It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter.

PORTS There are 3 ports in ATmega8: Port B, Port C,

Port D.Three registers are associated with every portDDRx – Data Direction RegisterPINx – Port inputPORTx- Port output

Where x would be either B,C or D.

PORT B(PB7-PB0)

It is a 8-bit bi-directional I/O port.It has internal pull up resistors(selected for

each bit).It can be used either as a input port or as

output port ( direction must be specified in programming).

PORT C(PC6-PC0)

It is a 7-bit bi-directional I/O port.It has internal pull up resistors(selected for

each bit).It can be used either as a input port or as

output port ( direction must be specified in programming).

PORTD(PD7-PD0)

It is a 8-bit bi-directional I/O port.It has internal pull up resistors(selected for

each bit).It can be used either as a input port or as

output port ( direction must be specified in programming).

Registers to Communicate with I/O Ports

To communicate with the ports of Atmega8, we use three registers:

PINx PORTx DDRx

Where x would be either B,C or D.

REGISTER DESCRIPTION OF I/O PORTS

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DDRx Register

It stands for Data Direction Register.It is used to define Port as Input or Output.In order to make Port as Input Port:

DDRx=0x00 (In Hexadecimal) DDRx=0b00000000(In Binary)In order to make Port as output Port:

DDRx=0xFF (In Hexadecimal) DDRx=0b11111111(In Binary)

PORTx RegisterIf DDRx=0xFF(Output port) Writing logic 1 to PORTx will make output

high i.e 5v for that particular pin.

Writing 0 to PORTx will make output low i.e 0v for that particular pin.

Continued..If DDRx=Ox00(Input port): If corresponding PORTx bit is set to 1, Internal

pull up resistors are enabled i.e if we do not connect this pin to anything it still reads as 1.

If corresponding PORTx bit is set to 0, internal pull up resistors are disabled i.e the pin will enter a high impedance state and will become unpredictable.

PINx Register

It reads data from the port pins.If any/all bits of DDRx is set to 0(input)for a

particular pin, we can read data from PINxIf any/all bits of DDRx is set to 1(output), then

reading PINx register gives the same data which has been output on that particular pin.

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